The present invention is related to a hand tool, and more particularly to a screwdriver with changeable operation modes. In accordance with the loosened and tightened states of the screw, the operation modes of the screwdriver can be changed.
A conventional screwdriver has a stem and a handle on which the stem is directly fixedly connected. When a user operates such screwdriver for screwing a screw, the user""s hand must repeatedly hold and release to rotate the screwdriver. This is inconvenient for the user. A ratchet screwdriver has been developed, wherein a ratchet mechanism is connected between a handle and a stem. When turning the handle in one direction, via the ratchet mechanism, the stem is synchronously rotated. When turning the handle in another direction, the handle idles without driving the stem. Accordingly, by means of reciprocally rotating the handle, the screw is one-way screwed. This is more convenient for a user to operate the screwdriver.
However, it is known that when screwing a screw with a ratchet screwdriver, the ratchet screwdriver fails to provide ratchet effect during the entire operation. This is because that during the screwing operation, no matter whether screwing or unscrewing the screw, there are two states, that is, loosening and tightening states. Only when the screw is in a tightened state to a certain extent, the ratchet screwdriver can provide ratchet effect. That is, only when the stem suffers a certain resistance, the ratchet mechanism can effectively work to provide ratchet effect. (that is, when the handle is turned in one direction, the handle idles without driving the stem, while when the handle is turned in another direction, the stem is driven.)
When the screw is in a loosened state, the resistance against the stem is insufficient to activate the ratchet mechanism. Under such circumstance, the ratchet screwdriver loses its ratchet effect, and it""s no different from a conventional screwdriver in operation. Therefore, the conventional ratchet screwdriver is still imperfect.
It is therefore a primary object of the present invention to provide a screwdriver with changeable operation modes. In accordance with the loosened and tightened states of the screw, the operation modes of the screwdriver can be changed. When the screwdriver is used to screw a screw in a loosened state, without turning the handle, a user can directly turn the stem to screw a screw. In the case that the screw is in a certain tightened state, the user can turn the handle to drive the stem.